Polysiloxane-containing tire rubber composition

ABSTRACT

A rubber composition for a tire comprising: 
     100 parts by weight of a starting rubber; 
     10 to 150 parts by weight of a carbon black; 
     0.1 to 20 parts by weight of a sulfur; and 
     40 parts by weight or less of a polysiloxane 
     having the following alkoxysilyl group (I) or acyloxysilyl group (II) and having an average degree of polymerization of 3 to 10,000: 
     
         .tbd.Si--OR.sup.1                                          (I) 
    
     
         .tbd.Si--OCOR.sup.2                                        (II) 
    
     wherein R 1  is a substituted or unsubstituted monovalent hydrocarbon group or an organic group containing an ether bond and having 1 to 18 carbon atoms and R 2  is hydrogen or a hydrocarbon group having 1 to 21 carbon atoms.

TECHNICAL FIELD

The present invention relates to a polysiloxane-containing rubbercomposition for a tire. More specifically, the present invention relatesto a rubber composition having improved processability and productivityand also the other improved properties, suitable for use as a cordcovering of a tire, carcass coat or belt cover of a tire, a bead filler,a side tread or an inner liner.

BACKGROUND ART

In pneumatic vehicle tires such as those for passenger cars, trucks, andbuses, a belt layer composed of a steel cord is arranged on a carcasslayer to receive the strong shock and load subjected during running of atire. One problem to be solved in a pneumatic vehicle tire is to improvethe processability of a rubber composition for covering a steel cord toimprove the productivity of a tire. From this viewpoint, it has beentried to increase the amount of a process oil to be compounded or todecrease the amount of a carbon black to be compounded to decrease theviscosity of unvulcanized rubber composition. However, these proposalshave the problems of decreasing the properties, such as hardness, of thevulcanized rubber. Furthermore, it may be possible to add processingaids, processing aids capable of providing the sufficient results havenot been known yet.

Further, it has been tried to increase the compounding amount of aprocess oil and to decrease the compounding amount of a carbon black forthe purpose of improving the processability and productivity of rubbercompositions for carcass coat or belt cover or bead filler or furtherfor inner liner of a pneumatic tire such as for passenger cars, trucksand buses, so as to decrease the viscosity of the unvulcanizer rubbercomposition. However, these processes cause the problems of decreasingthe physical properties of vulcanizates such as hardness, E' (storagemodulus), tanδ, although the viscosity of the unvulcanized rubbercomposition is decreased. Furthermore, it is also considered to use theaddition of a processing aid, there are no existent processing aids, inthe prior art, capable of attaining the above purpose without impairingthe vulcanized physical properties.

Furthermore, as one problem to be solved in a tire for a passenger car,truck, bus etc. is to decrease the rolling resistance of a tire and alsoto decrease the heat generation of a tire. From this viewpoint, it hasbeen proposed that, as a reinforcing agent for a rubber composition fora side tread of a tire, a special carbon black is used or a part of thecarbon black is replaced with silica. However, when the silica is usedas a reinforcing agent, there occur problems such as the mixingprocessability of unvulcanized rubber compounding composition and thedispersibility thereof becomes poor with the increase in the compoundingamount of silica, although the rolling resistance can be decreased.

Furthermore, a rubber compounding composition containing clay (i.e.,water-containing aluminum silicate) is used as a rubber for, forexample, a head insulation and a white side tread of a tire such as apassenger car, truck, bus. Such a rubber composition is desired toimprove the processability (e.g., the prevention of burning of rubberat, for example, extrusion step and compression step, the improvement inthe production line speed) and to increase the productivity. For thispurpose, although it is considered that the compounding amount ofprocess oil is increased, or the compounding amount of carbon black isdecreased, there occur problems such as the vulcanized physicalproperties such as hardness and strength are impaired, although theviscosity of the unvulcanized compounding composition is decreased.Furthermore, processing aids capable of attaining the above purpose isnot known in the art.

DISCLOSURE OF INVENTION

Accordingly, the first object of the present invention is to eliminatethe above-mentioned problems of the conventional rubber composition forcovering a steel cord and to provide a rubber composition for covering asteel cord, capable of improving the processability of the unvulcanizedrubber composition by the decrease in the viscosity and the extension ofthe scorching time and by the increase in the productivity by theshortening of the vulcanization time, without substantially impairingthe properties of the vulcanizate such as the hardness, tanδ, etc.

A second object of the present invention is to eliminate theabove-mentioned problems of the conventional rubber composition forcarcass coat or belt cover and to provide a rubber composition forcarcass coat or belt cover of tire, capable of improving theprocessability of the unvulcanized compounding composition by thedecrease in the viscosity and the extension in the scorching time and ofimproving the productivity by the shortening of the vulcanization time,without substantially impairing the vulcanized physical properties suchas the hardness and tanδ.

A third object of the present invention is to eliminate theabove-mentioned problems of the conventional rubber composition for beadfiller and to provide a rubber composition for a bead filler of a tire,capable of improving the processability of the unvulcanized compoundingcomposition by the decrease in the viscosity and extension of scorchingtime, etc. and of improving the productivity by the shortening of thevulcanization time, without substantially impairing the vulcanizedphysical properties such as E' (storage modulus) and tanδ.

A fourth object of the present invention is to eliminate theabove-mentioned problems of the conventional silica-containing rubbercomposition for a side tread of a tire and to provide a rubbercomposition for a side tread of a tire capable of improving the rollingresistance and the flex fatigue resistance, without substantiallyworsening the mixing processability and dispersibility of theunvulcanized rubber compounding composition even if the silica iscompounded.

A fifth object of the present invention is to eliminate theabove-mentioned problems of a rubber composition for an inner liner andto provide a rubber composition for an inner liner of a tire, capable ofimproving the processability of the unvulcanized rubber composition bythe decrease in the viscosity and the extension in the scorching timeand of improving the productivity by shortening the vulcanization time,without substantially impairing the vulcanized physical properties suchas E' (storage modulus) and tanδ.

A sixth object of the present invention is to eliminate theabove-mentioned problems of the conventional clay-containing rubbercomposition and is to provide a clay-containing rubber compositioncapable of improving the processability and productivity by the decreasein the viscosity of the unvulcanized compounding composition and by theextension of the scorching time, without substantially impairing thevulcanized physical properties such as the hardness and breakingstrength.

In accordance with the present invention, there is provided a rubbercomposition for a tire comprising:

100 parts by weight of a starting rubber;

10 to 150 parts by weight of a carbon black;

0.1 to 20 parts by weight of a sulfur; and

40 parts by weight or less of a polysiloxane

having the following alkoxysilyl group (I) or acyloxysilyl group (II)and having an average degree of polymerization of 3 to 10,000:

    .tbd.Si--OR.sup.1                                          (I)

    .tbd.Si--OCOR.sup.2                                        (II)

wherein R¹ is a substituted or unsubstituted monovalent hydrocarbongroup or an organic group containing an ether bond and having 1 to 18carbon atoms and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.

BEST MODE FOR CARRYING OUT THE INVENTION

The starting rubber of the rubber composition for a tire according tothe present invention may be any diene rubber generally used for tiresin the past, for example, natural rubber (NR), polyisoprene rubber (IR),various polybutadiene rubbers (BR), various styrene-butadiene copolymerrubbers (SBR). These diene rubbers may be used alone or in any blendsthereof.

The polysiloxane containing the alkoxysilyl groups (I) or acyloxysilylgroups (II) compounded in the rubber composition according to thepresent invention, as mentioned above, must have an alkoxysilyl group(I) or acyloxysilyl group (II) be a polymer (or oligomer) having anaverage degree of polymerization of 3 to 10,000, preferably 10 to 1,000.Accordingly, in the polysiloxane of the present invention, it isessential that a .tbd.Si--O-- R¹ group or .tbd.Si--OCOR group bepresent. These groups may be at the main chain, side chains, or ends.Further, a hydrogen group or other organic groups are also possible. Inaddition, the presence of at least 6 OR¹ group and OCOR² group in themolecule thereof, namely at least 6 alkoxy and acyloxy groups preferablydirectly bonded to the Si atom in the main chain in one moleculethereof. The polysiloxane usable in the present invention preferably hasat least one hydrocarbon group, preferably alkyl group directly bondedto the Si atom in the molecule thereof in view of the affinity thereofwith the rubber component. The polysiloxane is a known substance. Forexample, it may be manufactured as follows:

The polysiloxane containing an alkoxysilyl or acyloxysilyl group issynthesized by reacting an Si--H group-containing polysiloxane andalcohol or carboxylic acid in the presence of a catalyst.

As the .tbd.Si--H group containing polysiloxane, the following may beillustrated. ##STR1##

As the above-mentioned alcohol, methanol, ethanol, propanol, butanol,pentanol, heptanol, octanol, octadecanol, phenol, benzyl alcohol, etc.,and also alcohols having oxygen atoms such as ethylene glycol monomethylether, diethylene glycol monomethyl ether may be illustrated.

As the carboxylic acid, acetic acid, propionic acid, palmitic acid,stearic acid, myristic acid, etc. may be mentioned.

As the catalyst, chloroplatinic acid, platinum-ether complexes,platinum-olefin complexes, PdCl₂ (PPh₃)₂, RhCl₂ (PPh₃)₂ may be used. Thecorresponding .tbd.Si--H group-containing polysiloxane and alcohol orcarboxylic acid are reacted in the presence of the catalyst forsynthesis. As the method for introducing the organic group, introductionis easily carried out by reacting .tbd.Si--H and an organic compoundhaving a double bond using the above catalyst. As a compound having adouble bond, there are styrene, α-methylstyrene, α-methylstyrene dimer,limonene, vinylcyclohexene, etc.

As another method, synthesis is possible by causing a reaction between acorresponding .tbd.Si--H group-containing polysiloxane and a doublebond-containing alkoxysilane as shown below in the presence of the abovecatalyst: ##STR2##

As still another method, the polysiloxane used in the present inventionmay be synthesized by reacting a silanol terminal polysiloxane and analkoxysilane in the presence of a catalyst, for example, a bivalent tincompound. Examples of such a silanol terminal polysiloxane are: ##STR3##wherein n is 1 to 2000.

Examples of the alkoxysilane are the following alkoxysilanes. Further,the silane coupling agents shown in Table I are exemplified. ##STR4##

                  TABLE I                                                         ______________________________________                                        Chemical name  Structural formula                                             ______________________________________                                        Vinyltrimethoxysilane                                                                        CH.sub.2 ═CHSi(OCH.sub.3).sub.3                              Vinyltriethoxysilane CH.sub.2 ═CHSi(OCH.sub.2 CH.sub.3).sub.3                           Vinyltris(2- CH.sub.2 ═CHSi(OCH.sub.2 CH.sub.2                           OCH.sub.3).sub.3                                                 methoxyethoxy)silane                                                           - N-(2-aminoethyl)3-  aminopropylmethyl-  dimethoxysilane                     - N-(2-aminoethyl)3- H.sub.2 NCH.sub.2 CH.sub.2 NH(CH.sub.2).sub.3                        Si(OCH.sub.3).sub.3                                              aminopropyltrimethoxy-                                                        silane                                                                        3-aminopropyltrimethoxy- H.sub.2 N(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3                      silane                                                           - 3-glycidoxypropyltri-  methoxysilane                                                      #STR5##                                                         - 3-glycidoxypropylmethyl-  dimethoxysilane                                                 #STR6##                                                         - 2-(3,4-  epoxycyclohexyl)ethyl-  trimethoxysilane                                         #STR7##                                                         - 3-methacryloxypropyl-  trimethoxysilane                                                   #STR8##                                                         - 3-mercaptopropyl- HS(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3                   trimethoxylsilane                                                             3-aminopropyl- H.sub.2 N(CH.sub.2).sub.3 Si(OCH.sub.2 CH.sub.3).sub.3                       triethoxysilane                                                 bis-[3-(triethoxysilyl)- [(CH.sub.3 CH.sub.2 O).sub.3 Si(CH.sub.2).sub.3                    .brket close-st..sub.2 S.sub.4                                  propyl]tetrasulfide                                                         ______________________________________                                    

The polysiloxane usable in the present invention may further besynthesized by a reaction between polysiloxane having a reactivefunctional group at its side chain or terminal and a silane couplingagent of Table I. Examples of the polysiloxane having a reactivefunctional group, are an epoxy group, amine group, mercapto group,carboxyl group, etc.

Note that the polysiloxane used in the present invention, as explainedabove, is not particularly limited in its terminal groups and sidechains and is determined by the type of the starting material usedduring manufacture.

The compounding amount of the polysiloxane used in the present inventionis 40 parts by weight or less, preferably 0.01 to 20 parts by weight,more preferably 0.1 to 10 parts by weight, particularly preferably 0.1to 8 parts by weight, based on 100 parts by weight of the diene rubberin the rubber composition. When the content of the polysiloxane is toosmall, the desired effects cannot be obtained, whereas if too large,polysiloxanes not bonding with the silica will leak out from thevulcanized product in some cases.

In the present invention, when silica is compounded into the aboverubber composition, silane coupling agents may be further compounded.The silane coupling agent usable in the present invention may be anysilane coupling agent used together with silica fillers in the past. Thetypical examples thereof are shown in Table I. Of these,bis-[3-(triethoxysilica)-propyl]tetrasulfide is most preferred from theviewpoint of the processability. Further, the following specialsulfur-containing silane coupling agents shown in Table II below canalso be used.

                  TABLE II                                                        ______________________________________                                        Chemical name Structural formula                                              ______________________________________                                          3-Trimethoxysilylpropyl-  N,N-dimethyl  thiocarbamoyl-  tetrasulfide                        #STR9##                                                          - Trimethoxysilylpropyl-  mercaptobenz-thiazole  tetrasulfide                              #STR10##                                                         - Thiethoxysilylpropyl-  methacrylate-monosulfide                                          #STR11##                                                         - Dimethoxymethylsilyl-  propyl-N,N-  dimethylthiocarbamoyl-  tetrasulf                  ide                                                                            ##STR12##                                                      ______________________________________                                    

According to the first embodiment of the present invention, there isprovided a rubber composition for covering a steel cord comprising 100parts by weight of a diene rubber containing 40 parts by weight or moreof natural rubber, 2 to 10 parts by weight of sulfur and 10 parts orless of the above polysiloxane having an average degree ofpolymerization of 3-10000.

According to the preferred embodiment of the first embodiment of thepresent invention, the rubber composition for covering a steel cord, inwhich 0 to 2 parts by weight, in terms of a Co element, of a cobalt saltof an organic acid is contained in the composition.

According to the preferred embodiment of the first embodiment of thepresent invention, the rubber composition for covering a steel cord,wherein the composition further contains 1.0 to 5 parts by weight ofpartial self-condensation product of hexamethylolmelamine pentamethylether and 0.5 to 5 parts by weight of a cresol resin.

As the rubber component of the rubber composition used in the rubbercomposition for covering steel cord according to the first embodiment ofthe present invention, conventional diene rubber (e.g., natural rubber(NR), polyisoprene rubber (IR), polybutadiene rubber (BR),styrene-butadiene copolymer rubber (SBR), etc.) are used. The use ofnatural rubber having a high tensile strength is most preferable and, inthe present invention, among 100 parts by weight of diene rubber, 40parts by weight or more, more preferably 80 parts by weight or more, ofnatural rubber is preferably used.

As the reinforcing agent compounded in the rubber composition accordingto the first embodiment of the present invention, carbon black or carbonblack and silica can be used. As the carbon black, any carbon blackconventionally used as a carbon black for tires (e.g., carbon blacksobtained by, for example, oil furnace method) can be used. The amount ofthe carbon black compounded is as mentioned above, but preferably 30 to80 parts by weight, based upon 100 parts by weight of the diene rubber.Furthermore, silica (and optionally a silane coupling agent) can be usedinstead of the carbon black and the addition of silica is preferablebecause the heat generation is decreased and the belt durability isimproved.

According to the first embodiment of the present invention, for thepurpose of improving the processability, while the anti-water adhesiveresistance and the anti-cracking property are improved, the polymer (oroligomer) having the above alkoxysilyl group and/or acyloxysilyl grouphaving the formula (I) and/or (II) and having an average degree ofpolymerization of 3-10000, preferably 10-1000 is compounded preferablyin an amount of 10 parts by weight or less, more preferably in an amountof 0.1-8 parts by weight, based upon 100 parts by weight of the dienerubber.

When the silane coupling agent is compounded into the rubber compositionused in the first embodiment of the present invention, the amount of thesilane coupling agent can be decreased when compared with the prior artand the abrasion resistance can be further improved. The preferableamount of the silane coupling agent according to the present inventionis 40% by weight or less, more preferably 0.5 to 20% by weight, basedupon the amount of the silica compounded in the rubber composition. Whenthe amount of the silane coupling agent is too small, the desiredeffects are difficult to obtain, whereas when the amount is too large,it is not preferable because the burns of rubber (scorching) are likelyto occur during the mixing and extrusion steps.

In the rubber composition for steel cord cover according to the firstembodiment of the present invention, preferably 2-10 parts by weight,more preferably 4-10 parts by weight of sulfur, based upon 100 parts byweight of the diene rubber, is compounded. The sulfur usable in thepresent invention can be any sulfur, which is conventionally used in therubber composition. The amount of sulfur is too small, the adhesivenessto the metal becomes insufficient, whereas if too large, the changes inthe physical properties after aging becomes large and it is unpreferablylikely to decrease the durability.

In the rubber composition for steel cord cover according to the firstembodiment of the present invention, 0-2 parts by weight, preferably0.1-1 part by weight, in terms of Co element, based upon 100 parts byweight of the diene rubber, of a cobalt salt of an organic acid iscompounded, whereby the adhesiveness is increased. However, when theamount of the cobalt salt of an organic acid is too large, the furtherimprovement in the adhesiveness cannot be obtained.

Examples of the cobalt salt of an organic acid compounded in the rubbercomposition according to the first embodiment of the present inventionare cobalt salts of linear or branched monocarboxylic acids having 5 to20 carbon atoms such as cobalt naphthenate, cobalt stearate, cobaltoctylate, cobalt oleate etc.

As mentioned above, in the preferable embodiment of the firstembodiment, 1.0-5 parts by weight of the partial self-condensationproduct and 0.5 to 5 parts by weight of cresol resin are compounded toimprove the hardness and anti-water adhesiveness. These additives areknown in the art and are available as follows. For example Sumicanol 507(50% of partial condensate of hexamethylolmelamine pentamethyl ether iscontained, Sumitomo Chemical) and furthermore, Sumicanol 610(methacresol resin, Sumitomo Chemical) are available.

According to the second embodiment of the present invention, there isprovided a rubber composition for a tire carcass coat or belt covercomprising 100 parts by weight of a diene rubber containing 40 parts byweight or more of natural rubber, 20 to 120 parts by weight of a carbonblack preferably having a nitrogen specific surface area of 60 m² /g orless and 10 parts by weight or less of a polysiloxane having thefollowing alkoxysilyl group (I) or acyloxysilyl group (II) and having anaverage degree of polymerization of 3 to 10,000:

    .tbd.Si--OR.sup.1                                          (I)

    .tbd.Si--OCOR.sup.2                                        (II)

wherein R¹ is a substituted or unsubstituted monovalent hydrocarbongroup or an organic group containing an ether bond and having 1 to 18carbon atoms and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.

As the rubber component of the rubber composition used in the rubbercomposition for a tire carcass coat or belt cover according to thesecond embodiment of the present invention, conventional diene rubber(e.g., natural rubber (NR), polyisoprene rubber (IR), polybutadienerubber (BR), styrene-butadiene copolymer rubber (SBR), etc.) are used.The use of natural rubber having a high tensile strength is mostpreferable and, in the present invention, among 100 parts by weight ofdiene rubber, 40 parts by weight or more, more preferably 60 parts byweight or more, of natural rubber is preferably used.

As the carbon black compounded in the rubber composition according tothe second embodiment of the present invention, among carbon blacksconventionally used as a carbon black for tires (e.g., carbon blacksobtained by, for example, oil furnace method), those having a nitrogenspecific surface area (N₂ SA) (determined by method C of ASTM-D3037-78)of 60 m^(2/) g or less, preferably 20-50 m² /g are used from theviewpoint of the heat generation. The nitrogen specific surface area ofthe carbon black of more than 60 m² /g causes the increase in tanδ andthis is not preferable because the heat generation tends to be worsen.

The amount of the carbon black compounded in the rubber composition usedin the second embodiment of the present invention is preferably 20-120parts by weight, more preferably 20-80 parts by weight, based upon 100parts by weight of the diene rubber. When the compounding amount of thecarbon black is too small, unpreferably the tensile strength and thephysical properties at break are possibly decreased. Contrary to this,when the compounding amount of the carbon black is too large, it is notpreferable because the viscosity of the rubber compounding product isincreased and therefore the processability becomes poor and the heatgeneration is increased.

In the rubber composition according to the second embodiment of thepresent invention; any silica, which is conventionally compounded in arubber composition, can be compounded, instead of a part of the carbonblack, in the rubber composition according to the second embodiment ofthe present invention and a silane coupling agent can be used togetherwith the silica.

According to the second embodiment of the present invention, the polymer(or oligomer) having the alkoxysilyl group and/or acyloxysilyl grouphaving the above formula (I) and/or (II) and having an average degree ofpolymerization of 3-10000, preferably 10-1000 is compounded preferablyin an amount of 10 parts by weight or less, more preferably in an amountof 0.1-8 parts by weight, based upon 100 parts by weight of the dienerubber, in the rubber composition for a tire carcass coat or cover.

When the silane coupling agent is compounded into the rubber compositionused in the second embodiment of the present invention, the amount ofthe silane coupling agent, the preferable amount of the silane couplingagent is 40% by weight or less, more preferably 0.5 to 20% by weight,based upon the amount of the silica compounded in the rubbercomposition. When the amount of the silane coupling agent is too large,it is not preferable because the burns of rubber (scorching) are likelyto occur during the mixing and extrusion steps.

According to the third embodiment of the present invention, there isprovided a rubber composition for a tire bead filler comprising 100parts by weight of a diene rubber containing 40 parts by weight or moreof natural rubber, 50 parts by weight or more of carbon black having anitrogen specific surface area of 100 m² /g or less and 10 parts byweight or less of the above polysiloxane containing the abovealkoxysilyl group (I) or acyloxysilyl group (II) and having an averagedegree of polymerization of 3-10000.

As the rubber component of the rubber composition used in the rubbercomposition for a tire bead filler according to the third embodiment ofthe present invention, conventional diene rubber (e.g., natural rubber(NR), polyisoprene rubber (IR), polybutadiene rubber (BR),styrene-butadiene copolymer rubber (SBR), etc.) are used. The use ofnatural rubber having a high tensile strength is most preferable and, inthe present invention, among 100 parts by weight of diene rubber, 40parts by weight or more, more preferably 70 parts by weight or more, ofnatural rubber is preferably used.

As the carbon black compounded in the rubber composition according tothe third embodiment of the present invention, among carbon blacksconventionally used as a carbon black for tires (e.g., carbon blacksobtained by, for example, oil furnace method), those having a nitrogenspecific surface area (N₂ SA) (determined by method C of ASTM-D3037-78)of 100 m² /g or less, preferably 70-90 m² /g are used from the viewpointof the heat generation. The nitrogen specific surface area of the carbonblack of more than 100 m² /g causes the increase in tanδ and this is notpreferable because the heat generation tends to be worsen.

The amount of the carbon black compounded in the rubber composition usedin the third embodiment of the present invention is preferably 50-120parts by weight, more preferably 55-80 parts by weight, based upon 100parts by weight of the diene rubber. When the compounding amount of thecarbon black is too small, unpreferably the tensile strength and thephysical properties at break are possibly decreased. Contrary to this,when the compounding amount of the carbon black is too large, it is notpreferable because the viscosity of the rubber compounding product isincreased and therefore the processability becomes poor and the heatgeneration is increased.

In the rubber composition according to the present invention; anysilica, which is conventionally compounded in a rubber composition, canbe compounded, instead of a part of the carbon black, in the rubbercomposition according to the third embodiment of the present inventionand a silane coupling agent can be used together with the silica. Thecompounding of the silica is preferable because the heat generation isdecreased and the durability is improved.

According to the third embodiment of the present invention, the polymer(or oligomer) having the alkoxysilyl group and/or acyloxysilyl grouphaving the above formula (I) and/or (II) and having an average degree ofpolymerization of 3-10000, preferably 10-1000 is compounded preferablyin an amount of 10 parts by weight or less, more preferably in an amountof 0.1-8 parts by weight, based upon 100 parts by weight of the dienerubber, in the rubber composition for a tire bead filler.

When the silane coupling agent is compounded into the rubber compositionused in the third embodiment of the present invention, the amount of thesilane coupling agent, the preferable amount of the silane couplingagent is 40% by weight or less, more preferably 0.5 to 20% by weight,based upon the amount of the silica compounded in the rubbercomposition. When the amount of the silane coupling agent is too large,it is not preferable because the burns of rubber (scorching) are likelyto occur during the mixing and extrusion steps.

According to the fourth embodiment of the present invention, there isprovided a rubber composition for a tire side tread comprising 100 partsby weight of a diene rubber containing 40 parts by weight or more ofpolybutadiene, preferably 0-50 parts by weight, more preferably 5-50parts by weight of silica and preferably 10-60 parts by weight of carbonblack, provided that the total amount of the silica and the carbon blackis 20-80 parts by weight, and the polysiloxane having the abovealkoxysilyl group (I) or acyloxysilyl group (II) such that at least 6alkoxy groups or at least 2 acyloxy groups, directly bonded to the Siatom are present in the molecule thereof and having an average degree ofpolymerization of 3-10,000 in an amount of 40% by weight or less, basedupon the amount of the silica.

According to the fourth embodiment of the present invention, 40% byweight or less of, based upon the compounding amount of silica, a silanecoupling agent is further compounded in the rubber composition for theside tread.

As the rubber component of the rubber composition used in the rubbercomposition for the side tread according to the fourth embodiment of thepresent invention, conventional diene rubber (e.g., natural rubber (NR),polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadienecopolymer rubber (SBR), etc.) are used. However, the use of the dienerubber containing 40 parts by weight or more of polybutadiene based upon100 parts by weight of the total diene rubber is preferable for the sidetread of a tire.

The silica compounded in the rubber composition to be used in the fourthembodiment of the present invention may be any silica conventionallyused for a tire (e.g., silicic acid hydrate obtained by a dry or wetprocess, nitrogen specific surface area 50-300 m² /g silica). Thecompounding amount of the silica is 5-50 parts by weight, preferably10-40 parts by weight, based upon 100 parts by weight of the rubber.When the compounding amount of the silica is too small, the sufficientdecrease in the rolling resistance cannot be obtained. Contrary to this,when the amount of the silica is too small, it is not preferable becausethe physical properties such as the tensile strength, physicalproperties at break are possibly decreased.

As the carbon black compounded in the rubber composition according tothe fourth embodiment of the present invention, any carbon blacksconventionally used as a carbon black for tires (e.g., carbon blacksobtained by, for example, oil furnace method) are used. The preferablecarbon blacks usable in the present invention are those having anitrogen specific surface area (N₂ SA) (determined by method C ofASTM-D3037-78) of 100 m² /g or less, preferably 30-90 m² /g and a DBPoil absorption (determined by a method according to ASTM-D-3493) of 70ml/100 g or more, more preferably 80-130 ml/100 g, from the viewpoint ofthe abrasion resistance.

The amount of the carbon black compounded in the rubber composition usedin the fourth embodiment of the present invention is preferably 10-60parts by weight, more preferably 20-50 parts by weight, based upon 100parts by weight of the diene rubber. In addition, the total compoundingamounts of the carbon black and the silica are preferably 20-80 parts byweight, more preferably 30-60 parts by weight. When the compoundingamount of the carbon black is too small, unpreferably the tensile stressat elongation and the physical properties at break are possiblydecreased. Contrary to this, when the compounding amount of the carbonblack is too large, it is not preferable because the viscosity of therubber compounding product is increased and therefore the processabilitybecomes poor and the heat generation is increased.

According to the fourth embodiment of the present invention, the polymer(oligomer) having the alkoxysilyl group and/or acyloxysilyl grouprepresented by the formula (I) and/or (II) and having an average degreeof polymerization of 3-10000, preferably 10-1000 is compounded in anamount of 40% by weight or less, preferably 0.5-20% by weight, basedupon the compounding amount of silica.

As mentioned above, although the vulcanized physical properties of theside tread of a tire having the silica are good, there are disadvantagesthat the processability during the unvulcanized state is poor. Inaccordance with our understandings, this is due to the presence of thesilanol group (.tbd.Si--OH) present on the surface of the silica.Namely, the structural product is formed in the rubber composition dueto the cohesive power of the silanol group to thereby increase theviscosity, the vulcanization accelerator etc. are adsorbed due to thepolarity of the silanol group to thereby delay the vulcanization, andthe kneading performance of the mixing is decreased due to theinsufficient compatibility with non-polar rubber. For these phenomena,the processability of the unvulcanized rubber composition is decreased.Furthermore, a silane coupling agent is often used, in combination withthe silica in the silica-compounding rubber composition for the purposeof the reinforcement of rubber. In such a case, since the silanol groupspresent in the inner pores of silica powder particles are interactedwith the silane coupling agent, whereby the silane coupling agent islost and the reinforcing effects are decreased, and therefore, a largeramount of the silane coupling agent should be disadvantageouslycompounded. As in the prior art, when a polar substance such asdiethylene glycol is added thereto, the adsorption of, a polar additivesuch as a vulcanization accelerator can be prevented to a certainextent, but this phenomenon cannot be completely prevented and thebonding of a substance such as a silane coupling agent, which should bechemically bonded to the silica particles, to the inner pores of thesilica cannot be prevented.

Nevertheless, according to the fourth embodiment of the presentinvention, since the polysiloxane having the alkoxysilyl group oracyloxysilyl group represented by the above formula (I) or (II) iscompounded in a rubber composition, the alkoxysilyl group (I) or theacyloxysilyl group (II) is reacted with the silanol group to therebycover the surface of the filler particles, and therefore, the problemsof the prior art are completely solved. Thus, the increase in theviscosity of the unvulcanized rubber composition caused by the cohesivepower and polarity of the silanol group and the wasteful consumption of,for example, polar additives such as a vulcanization accelerator or asilane coupling agent can be effective suppressed.

When the silane coupling agent is compounded into the rubber compositionused in the fourth embodiment of the present invention, the amount ofthe silane coupling agent can be decreased when compared with the priorart and the abrasion resistance can be further improved. The preferableamount of the silane coupling agent according to the present inventionis 40% by weight or less, more preferably 1 to 20% by weight, based uponthe amount of the silica compounded in the rubber composition. When theamount of the silane coupling agent is too small, the desired effectsare difficult to obtain, whereas when the amount is too large, it is notpreferable because the burns of rubber (scorching) are likely to occurduring the mixing and extrusion steps.

According to the fifth embodiment of the present invention, there isprovided a rubber composition for an inner liner rubber comprising 100parts by weight of a rubber component containing 50 parts by weight ormore of butyl rubber and 50 parts by weight or less of a diene rubber,preferably 20 to 120 parts by weight of a carbon black having a nitrogenspecific surface area of 60 m² /g or less, and preferably 10 parts byweight or less of polysiloxane having the above alkoxysilyl group (I) oracyloxysilyl group (II) and having an average degree of polymerizationof 3-10000.

As the rubber component of the rubber composition used in the rubbercomposition for an inner liner of a tire according to the fifthembodiment of the present invention, conventional diene rubber (e.g.,natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber(BR), styrene-butadiene copolymer rubber (SBR), etc.) and a butyl rubber(IIR) compounded thereto are used. In the present invention, in order tokeep the air holding property the butyl rubber should be compounded inan amount of 50 parts by weight or more, preferably 70 parts by weightor more, based upon 100 parts by weight of the rubber content. As theother rubber component, in view of the flex resistance, the use of dienerubber, especially natural rubber (NR), polyisoprene rubber (IR),polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR),etc. is preferable.

As the carbon black compounded in the rubber composition according tothe fifth embodiment of the present invention, among carbon blacksconventionally used as a carbon black for tires (e.g., carbon blacksobtained by, for example, oil furnace method), those having a nitrogenspecific surface area (N₂ SA) (determined by method C of ASTM-D3037-78)of 60 m² /g or less, preferably 20-40 m² /g are used from the viewpointof the heat generation. The nitrogen specific surface area of the carbonblack of more than 60 m² /g causes the increase in tanδ and this is notpreferable because the heat generation tends to be worsen.

The amount of the carbon black compounded in the rubber composition usedin the fifth embodiment of the present invention is preferably 20 to 120parts by weight, more preferably 30 to 70 parts by weight, based upon100 parts by weight of the rubber component. When the compounding amountof the carbon black is too small, there is a case where the stressduring elongation and the physical properties at break are unpreferablydecreased. Contrary to this, when the amount of carbon black is toolarge, it is not preferable that the viscosity of the rubber compoundingcomposition is likely increased to cause the poor processability and theheat generation becomes high.

In the rubber composition according to the fifth embodiment of thepresent invention, silica conventionally used in a rubber compositioncan be used, as a reinforcing agent, instead of a part of the carbonblack and a silane coupling agent can be used, together with the silica.

According to the fifth embodiment of the present invention, in therubber composition for a tire inner liner, the polymer (or oligomer)having the alkoxysilyl group and/or acyloxysilyl group having the aboveformula (I) and/or (II) and having an average degree of polymerizationof 3-10000, preferably 10-1000 is compounded preferably in an amount of10 parts by weight or less, more preferably in an amount of 0.1-8 partsby weight, based upon 100 parts by weight of the rubber component.

When the silane coupling agent is compounded into the rubber compositionused in the fifth embodiment of the present invention, the amount of thesilane coupling agent is 40% by weight or less, more preferably 1 to 20%by weight, based upon the amount of the silica compounded in the rubbercomposition. When the amount of the silane coupling agent is too large,it is not preferable because the burns of rubber (scorching) are likelyto occur during the mixing and extrusion steps.

According to a sixth embodiment of the present invention, there isprovided a clay compounding rubber composition comprising 5 to 100 partsby weight, based upon 100 parts by weight of the starting rubber, ofclay and 40 parts by weight or less, of polysiloxane based upon theamount of the clay, having the above alkoxysilyl group and/oracyloxysilyl group having the formula (I) or (II) and having an averagedegree of polymerization of 3-10000.

The rubber component of the clay-compounding rubber composition for atire according to the sixth embodiment of the present invention is notspecifically limited, and therefore, conventional diene rubber such asnatural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber(BR), styrene-butadiene copolymer rubber (SBR) acrylonitrile-butadienecopolymer rubber (NBR, etc.) are used. In addition, as in the case of arubber for white side tread, when the weather resistance is especiallyrequired, ethylene-propylene-diene terpolymer rubber (EPDM) and butylrubber (IIR) are preferably compounded as a part of the rubbercomponent.

The clay compounded in the rubber composition according to the sixthembodiment of the present invention may be any conventional clays usedfor a tire (e.g., kaoline clay mainly composed of aluminum silicatehydrate celsite clay, pyroferite clay, etc.). The compounding amount ofclay is 5-100 parts by weight, preferably 20-60 parts by weight, basedupon 100 parts by weight. When the compounding amount of clay is toosmall, the balance between the hardness and the physical properties atbreak becomes worse. Contrary to this, when the amount is too large, itis not preferable that the viscosity of the rubber compoundingcomposition is increased, whereby the processability is possibly worsen.

In the clay-compounding rubber composition according to the sixthembodiment of the present invention, any conventional carbon black usedfor a tire can be used and the compounding amount thereof is preferably50-90 parts by weight, based upon 100 parts by weight of rubber.

In the clay-compounding rubber composition according to the sixthembodiment of the present invention, the polymer (or oligomer) havingthe alkoxysilyl group and/or acyloxysilyl group having the above formula(I) and/or (II) and having an average degree of polymerization of3-10000, preferably 10-1000 is compounded in an amount of 40% by weight,preferably 0.5 to 20% by weight, based upon the compounding amount ofthe clay.

Namely, according to the sixth embodiment of the present invention,since the alkoxysilyl group (I) or acyloxysilyl group (II) is reactedwith the moiety of silicic acid hydrate in the clay by compounding, intothe rubber composition, the polysiloxane having the alkoxysilyl group(I) or acyloxysilyl group (II), the non-polarity of the silicic acidhydrate moiety is made polarity, the anti-cracking property and theprocessability of the clay-compounding rubber composition can beimproved.

When the silane coupling agent is compounded into the rubber compositionused in the sixth embodiment of the present invention, the amount of thesilane coupling agent can be decreased when compared with the prior artand the abrasion resistance can be further improved. The preferableamount of the silane coupling agent according to the present inventionis 40% by weight or less, more preferably 0.5 to 20% by weight, basedupon the amount of the silica in the rubber composition.

The rubber composition according to the present invention may contain,in addition to the above-mentioned essential ingredients, avulcanization or cross-liking agent, a vulcanization or cross-linkingaccelerator, various types of oils, an antiaging agent (or antioxidant),plasticizer, or other various additives generally compounded in generalrubbers. The compounding compositions are kneaded and vulcanized bygeneral methods to make the composition which may then be used forvulcanization or cross-linking. The amounts of these additives added maybe made the amounts generally added in the past so long as they do notrun counter to the object of the present invention.

EXAMPLES

The present invention will now be further illustrated by, but thetechnical scope thereof is by no means limited to, the followingExamples.

Example I-1 to I-8 and Comparative Examples I-1 to I-5

The polysiloxanes used in the present invention were synthesized by thefollowing general methods:

Polysiloxane 1

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 60 g of methanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, and a reaction was carriedout at 80° C. for 10 hours. The estimated structure of the resultantcompound is as follows.

Polysiloxane 2

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 72 g of ethanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, and a reaction was carriedout at 80° C. for 10 hours. The estimated structure of the resultantcompound is as follows. ##STR13##

The other compounding components used in the compounding of each Exampleof the following Examples and Comparative Examples (see Table III)(parts by weight) were the following commercially available products.

                  TABLE III                                                       ______________________________________                                                  (wt. parts)                                                                     Comp.                  Comp.                                         Ex- Ex- Ex- Ex- Ex-                                                           ample ample ample ample ample                                                 I-1 I-1 I-2 I-2 I-3                                                        ______________________________________                                          NR (Natural Rubber) 100 100 100 100 100                                       Carbon black 63 63 63 63 63                                                   Silica --  -- -- -- --                                                        Silane coupling -- -- -- -- --                                                agent                                                                         Active agent -- -- -- -- --                                                   Polysiloxane-1 -- 2.0 4.0 -- 1.0                                              Polysiloxane-2 -- -- -- -- --                                                 Silicone oil -- -- -- -- --                                                   Aromatic oil 4.0 2.0 -- 4.0 3.0                                               Zinc oide 10.0 10.0 10.0 10.0 10.0                                            Antioxidant 1.0 1.0 1.0 1.0 1.0                                               Cobalt naphthenate 3.0 3.0 3.0 3.0 3.0                                        Sulfur 8.0 8.0 8.0 8.0 8.0                                                    Vulcanization 0.5 0.5 0.5 0.5 0.5                                             accelerator                                                                   Cresol resin -- -- -- 1.0 1.0                                                 Partial condensate -- -- -- 5.0 5.0                                           of hexamethylol                                                               melamine                                                                      pentamethyl                                                                   ether                                                                         Mooney viscosity 65 59 54 63 61                                               Scorching 28 30 32 29 30                                                      time (min)                                                                    Vulcanization 10.8 10.3 9.9 11.9 11.5                                         rate (min)                                                                    Hs (20° C.) 73 73 73 80 80                                             tanδ (60° C.) 0.19 0.19 0.19 0.20 0.20                           Initial 95 95 95 95 95                                                        adhesiveness (%)                                                              Adhesiveness 66 70 70 80 85                                                   against                                                                       hot water (%)                                                               ______________________________________                                                  (wt. parts)                                                                     Example  Example   Example                                                                              Example                                    I-4 I-5 I-6 I-7                                                            ______________________________________                                          NR (Natural Rubber) 100 100 100 100                                           Carbon black 63 63 63 43                                                      Silica --  -- -- 20                                                           Silane coupling -- -- -- 1.0                                                  agent                                                                         Active agent -- -- -- 1.3                                                     Polysiloxane-1 2.0 4.0 -- 2.0                                                 Polysiloxane-2 -- -- 2.0 --                                                   Silicone oil -- -- -- --                                                      Aromatic oil 2.0 -- 2.0 1.0                                                   Zinc oxide 10.0 10.0 10.0 10.0                                                Antioxidant 1.0 1.0 1.0 1.0                                                   Cobalt naphthenate 3.0 3.0 3.0 3.0                                            Sulfur 8.0 8.0 8.0 8.0                                                        Vulcanization 0.5 0.5 0.5 0.5                                                 accelerator                                                                   Cresol resin 1.0 1.0 1.0 1.0                                                  Partial condensate 5.0 5.0 5.0 5.0                                            of hexamethylol                                                               melamine                                                                      pentamethyl                                                                   ether                                                                         Mooney viscosity 58 54 59 59                                                  Scorching 3 32 31 31                                                          time (min)                                                                    Vulcanization 11.2 10.7 11.3 11.6                                             rate (min)                                                                    Hs (20° C.) 80 80 80 80                                                tanδ (60° C.) 0.20 0.20 0.20 0.16                                Initial 95 95 95 95                                                           adhesiveness (%)                                                              Adhesiveness 85 90 85 85                                                      against                                                                       hot water (%)                                                               ______________________________________                                                  (wt. parts)                                                                              Comp.     Comp.  Comp.                                      Example Example Example Example                                               I-8 I-3 I-4 I-5                                                            ______________________________________                                          NR (Natural Rubber) 100 100 100 100                                           Carbon black 43 63 63 59                                                      Silica 20 --  -- --                                                           Silane coupling -- -- -- --                                                   agent                                                                         Active agent 1.3 -- -- --                                                     Polysiloxane-1 2.0 -- -- --                                                   Polysiloxane-2 -- -- -- --                                                    Silicone oil -- 2.0 -- --                                                     Aromatic oil -- 2.0 8.0 4.0                                                   Zinc oxide 10.0 10.0 10.0 10.0                                                Antioxidant 1.0 1.0 1.0 1.0                                                   Cobalt naphthenate 3.0 3.0 3.0 3.0                                            Sulfur 8.0 8.0 8.0 8.0                                                        Vulcanization 0.5 0.5 0.5 0.5                                                 accelerator                                                                   Cresol resin 1.0 1.0 1.0 1.0                                                  Partial condensate 5.0 5.0 5.0 5.0                                            of hexamethylol                                                               melamine                                                                      pentamethyl                                                                   ether                                                                         Mooney viscosity 60 61 58 59                                                  Scorching 32 28 31 31                                                         time (min)                                                                    Vulcanization 11.9 9.7 12.3 12.4                                              rate (min)                                                                    Hs (20° C.) 80 -- 78 78                                                tanδ (60° C.) 0.16 -- 0.21 0.19                                  Initial 95 -- 95 95                                                           adhesiveness (%)                                                              Adhesiveness 85 -- 80 80                                                      against                                                                       hot water (%)                                                               ______________________________________                                    

Natural Rubber: RSS #1

Carbon black: Seast 300 (Tokai Carbon, N₂ SA 84 m² /g, DBP oilabsorption 75 ml/100 g)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Active agent: Diethylene glycol

Silicone oil: KF99 (Shinetsu Kagaku Kogyo K.K.)

Aromatic oil: Process oil X-140 (Kyodo Sekiyu)

Zinc oxide: Zinc white R (Toho Aen)

Antioxidant: Antigen 6C (Sumitomo Chemical Co.)(N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine)

Cobalt naphthenate: Dainihon Ink Chemical Co. (10% by weight of Coelement is contained)

Vulcanization accelerator: Accel DZ-G (Kawaguchi Chemical Ind.)(N,N'-dicyclohexyl-2-benzothiazolsulfenamide)

Sulfur: Insoluble sulfur (20% oil treatment)

Cresol resin: Sumicanol 610 (Sumitomo Chemical Co.)

Partial condensate of hexamethylol melamine penta methyl ether:Sumicanol 507 (Sumitomo Chemical Co.) (50% of said condensate isincluded.)

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece and thevulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties of the compositions obtained in each Examples wereas follows:

Mooney viscosity

Measured the viscosity at 100° C. according to JIS K 6300.

Scorching time

Time for viscosity to rise 5 points at 125° C. measured according to JISK 6300.

Vulcanization rate

Time to reach 95% vulcanization at 160° C. measured according to JIS K6300.

Hardness (Hs)

Measured the hardness at 20° C. according to JIS K 6301

tanδ

Measured by viscoelasticity spectrometer (made by Toyo Seiki Seisakusho)at 20 Hz, initial elongation of 10%, and dynamic strain of ±2%.

Initial Adhesiveness

From the both sides of brass plated steel cords (1×5 structure) arrangedin a parallel fashion with a distance of 12.5 mm, the rubber compositionwas filled therein by coating and the fabric having a width of 25 mm wasvulcanized at 170° C.×20 mm to prepare a test sample and the rubbercoating percentage (%) was evaluated by pulling out the wire accordingto ASTM-D-2229.

Adhesiveness against Hot Water

The decrease in the adhesiveness caused by the penetration of water fromthe outer damage was determined by cutting a lower end of the wire of asample for pulling out by hand and immersing in a hot water having atemperature of 70° C. After allowing to stand for 4 weeks, the wire waspulled out from the resultant sample and the rubber coating percentage(%) was evaluated, according to ASTM-D-2229.

The following evaluation results are shown in Table III, together withthe compounding compositions.

Comparative Example I-1 and I-2 are typical conventional compoundingcompositions.

Example I-1 to I-2 are those containing the polysiloxane, in addition toComparative Example I-1 and, due to the addition of the polysiloxane,the decrease in the viscosity, the extension in the scorching time andthe reduction in the vulcanization rate are observed and theprocessability are made good and, although Hs and tanδ are equivalent,the adhesiveness against water is also improved. Examples I-3 to I-6 arethose containing the polysiloxane, in addition to Comparative ExampleI-2, the results similar to the above-mentioned results of Examples I-1to I-2 are obtained. Examples I-7 to I-8 are those containing thesilica, in addition to Example I-4, the decrease in the heat generationand the improvement in the durability are observed.

On the other hand, Comparative Example I-3 contains a silicone oil,instead of the polysiloxane of Example I-4, the rubber sheet was foamed,and therefore, this was not practically used. Furthermore, althoughComparative Examples I-4-I-5 contain a further amount of the processoil, instead of the polysiloxane of Example I-4, and the amount of thecarbon black is decreased so as to intend to decrease the viscosity, Hswas decreased and the durability was also decreased.

As explained above, according to the first embodiment of the presentinvention, since, due to the incorporation of the polysiloxane togetherwith sulfur and cobalt into the rubber composition for coating steelcords, the viscosity of the unvulcanized rubber composition isdecreased, the scorching time is extended, and the vulcanization rate isincreased, the processability is largely improved, the hardness and tanδof the vulcanized product are more than equal and the adhesivenessagainst water can be improved.

Example II-1 to II-6 and Comparative Examples II-1 to II-6

The polysiloxane 1 and 2 used in the present invention were synthesizedaccording to the method described in Example I.

The other compounding components used in the compounding of thefollowing Examples and Comparative Examples (see Table IV) were thefollowing commercially available products.

                                      TABLE IV                                    __________________________________________________________________________           Comp.                       Comp.                                                                             Comp.                                                                             Comp.                                                                             Comp.                                                                             Comp.                        Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam-       ple ple ple ple ple ple ple ple ple ple ple ple                               II-1 II-1 II-2 II-3 II-4 II-5 II-6 II-2 II-3 II-4 II-5 II-6                 __________________________________________________________________________    NR     65  65  65  65  65  65  65  65  30  65  65  65                           SBR 25 25 25 25 25 25 25 25 60 25 25 25                                       BR 10 10 10 10 10 10 10 10 10 10 10 10                                        CB-1 60 60 60 60 60 30 30 30 60 --  60 60                                     CB-2 --  --  --  --  --  --  --  --  --  60 --  --                            Silica -- -- -- -- -- 20 20 -- -- --  -- --                                   Silane coupling -- -- -- -- -- 1.0 --  -- -- -- -- --                         agent                                                                         Active agent -- -- -- -- -- 1.3 1.3 -- -- -- -- --                            Polysiloxane-1 -- 1.0 2.0 4.0 -- 2.0 2.0 -- 2.0 2.0 -- --                     Polysiloxane-2 -- --  --  --  2.0 --  --  -- --  --  -- --                    Silicone oil -- -- -- -- --  -- -- 2.0 -- -- -- --                            Aromatic oil 8.0 7.0 6.0 4.0 6.0 3.0 -- 6.0 8.0 12.0 13.0 8.0                 Zinc oxide 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0                    Stearic acid 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                  Antioxidant 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                   Sulfur 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2                        Vulcanization 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2                 accelerator                                                                   Mooney 59 56 54 48 55 56 56 58 55 56 54 55                                    viscosity                                                                     Scorching 29 30 31 32 31 31 32 28 33 28 31 31                                 time (min)                                                                    Vulcanization 8.1 7.9 7.6 7.4 7.7 7.8 8.0 6.9 8.6 7.8 8.3 8.5                 rate (min)                                                                    Hs (20° C.) 62 62 62 62 62 62 62 --  62 62 59 59                       tanδ (20° C.) 0.14 0.14 0.14 0.14 0.14 0.13 0.13 -- 0.16                                                          0.17 0.15 0.13             __________________________________________________________________________

Natural Rubber: SIR-20

SBR: Nipol 1502 (Nihon Zeon)

BR: Nipol 1220 (Nihon Zeon)

Carbon black

CB-1: Seast V (Tokai Carbon, N₂ SA 27 m² /g)

CB-2: Seast 300 (Tokai Carbon, N₂ SA 84 m² /g)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Silicone oil: KF 99 (Shinetsu Kagaku Kogyo K.K.)

Zinc oxide: Zinc white #3 (Seido Kagaku)

Stearic acid: Lunac YA (Kao Soap Co.)

Antioxidant: Antigen 6C (Sumitomo Chemical Co.)(N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine)

Sulfur: Insoluble sulfur (20% oil treatment)

Vulcanization accelerator: Nocceler CZ (Ouchi Shinko Chemical IndustrialCo., Ltd.) (N-cyclohexyl-2-benzothiazylsulfenamide)

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece (rubbersheet) and the vulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties (Mooney viscosity, scorching time, vulcanizationrate, hardness Hs and tanδ) of the composition obtained in each Exampleare the same methods of the above-mentioned Example I.

The following evaluation results are shown in Table IV, together withthe compounding compositions. Note that Comparative Example II-1 is atypical conventional composition for carcass compounding.

Examples II-1 to II-6 are all within the range of the present inventionand all provide the good results. Namely, Examples II-1 to II-4 arethose containing the polysiloxane, in addition to Comparative ExampleII-1, the decrease in the viscosity of the unvulcanized compoundingcompositions and the extension of the scorch are observed and thevulcanization rate is reduced, the processability is made good, and thephysical properties such as hardness and tanδ are not substantiallyimpaired. Examples II-5 to II-6 are those containing silica, in additionto Example II-2, and therefore, the head generation is decreased and thedurability is improved.

On the other hand, Comparative Example II-2 contains the silicone oilinstead of the polysiloxane in Example II-2, the rubber sheet was foamedand cannot be practically used. Comparative Example II-3 contains thepolymer blend which is not within the definition of the presentinvention, compared with Example II-2, and therefore, the heatgeneration is worsen (i.e., the increase in tanδ). Comparative ExampleII-4 contains the carbon black which is not within the definition of thepresent invention, compared with Example II-2, and therefore, the heatgeneration is worsen. Comparative Examples II-5 to II-6 are intended todecrease the viscosity by increasing the amount of the oil anddecreasing the amount of the carbon black, when compared with ExampleII-2, it is not preferable because the hardness Hs is decreased and alsobecause the stiffness is decreased.

As explained above, according to the second embodiment of the presentinvention, the decrease in the viscosity of the unvulcanized compoundingcomposition, the desired results such as the improvement in theprocessability by the extension of the scorching time (prevention of theburning of the rubber in the extrusion and pressing steps, the increasein the line speed, etc.), or the improvement in the productivity by theshortening of the vulcanization step can be obtained, without impairingthe physical properties of the vulcanized products such as the hardnessHs, tanδ, etc. due to the compounding 20-120 parts by weight of thespecified carbon black and 10 parts by weight or less of the specifiedpolysiloxane to 100 parts by weight of the diene rubber containing 40parts by weight or more of natural rubber. According to the knownprocesses, e.g., the increase in the compounding amount of a process oiland the decrease in the compounding amount of a carbon black, althoughthe viscosity is decreased, the physical properties such as hardness arealso decreased, and therefore, these properties cannot be balanced.

Thus, the rubber composition according to the present invention issuitable for use as those for carcass coat of a bus tire or for a beltcover.

Example III-1 to III-7 and Comparative Examples III-1 to III-5

The polysiloxanes used in the present invention were synthesizedaccording to the method described in Example I.

The other compounding components used in the compounding of thefollowing Examples and Comparative Examples (see Table V) were thefollowing commercially available products.

                                      TABLE V                                     __________________________________________________________________________            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                    III-1 III-2 III-3 III-4 III-5 III-6 III-7                                  __________________________________________________________________________      NR 80 80 80 80 50 80 80                                                       SBR 20 20 20 20 50 20 20                                                      CB-1 70 70 70 70 68 50 50                                                     CB-2 -- -- -- -- -- -- --                                                     Silica -- -- -- -- -- 20 20                                                   Silane coupling -- -- -- -- -- 1.0 --                                         agent                                                                         Active agent -- -- -- -- -- 1.3 1.3                                           Polysiloxane-1 1.0 2.0 4.0 -- 2.0 2.0 2.0                                     Polysiloxane-2 -- -- -- 2.0 -- -- --                                          Silicone oil                                                                  Aromatic oil 7.0 6.0 4.0 6.0 6.0 5.0 4.0                                      Zinc oxide 5.0 5.0 5.0 5.0 5.0 5.0 5.0                                        Stearic acid 2.0 2.0 2.0 2.0 2.0 2.0 2.0                                      Antioxidant 1 0 1.0 1.0 1.0 1.0 1.0 1.0                                       Sulfur 3.5 3.5 3.5 3.5 3.5 3.5 3.5                                            Vulcanization 1.0 1.0 1.0 1.0 1.0 1.0 1.0                                     agent                                                                         Mooney viscosity 66 63 58 64 63 64 65                                         Scorching 23 24 25 24 26 24 25                                                time (min)                                                                    Vulcanization 7.7 7.5 7.2 7.6 7.8 7.6 7.8                                     rate (min)                                                                    E' (60° C.) (MPa) 7.3 7.3 7.3 7.3 7.3 7.4 7.3                          tanδ (60° C.) 0.19 0.19 0.19 0.19 0.19 0.15 0.15               __________________________________________________________________________            Comp.  Comp.  Comp.  Comp.  Comp.                                        Example Example Example Example Example                                       III-1 III-2 III-3 III-4 III-5                                              __________________________________________________________________________      NR 80 80 80 80 80                                                             SBR 20 20 20 20 20                                                            CB-1 70 70 -- 70 55                                                           CB-2 -- -- 70 -- --                                                           Silica -- -- -- -- --                                                         Silane coupling -- -- -- -- --                                                agent                                                                         Active agent -- -- -- -- --                                                   Polysiloxane-1 -- -- 2.0 -- --                                                Polysiloxane-2 -- -- -- -- --                                                 Silicone oil -- 2.0 -- -- --                                                  Aromatic oil 8.0 6.0 9.0 23.0 8.0                                             Zinc oxide 5.0 5.0 5.0 5.0 5.0                                                Stearic acid 2.0 2.0 2.0 2.0 2.0                                              Antioxidant 1.0 1.0 1.0 1.0 1.0                                               Sulfur 3.5 3.5 3.5 3.5 3.5                                                    Vulcanization 1.0 1.0 1.0 1.0 1.0                                             agent                                                                         Mooney viscosity 69 66 72 59 60                                               Scorching 22 21 23 24 24                                                      time (min)                                                                    Vulcanization 7.9 6.9 7.4 8.2 8.3                                             rate (min)                                                                    E' (60° C.) (MPa) 7.3 -- 7.5 4.9 4.8                                   tanδ (60° C.) 0.19 -- 0.22 0.20 0.17                           __________________________________________________________________________

Natural Rubber: SIR-20

SBR: Nipol 1502 (Nihon Zeon)

Carbon black

CB-1: Seast N (Tokai Carbon, N₂ SA 74 m² /g)

CB-2: Diablack A (Tokai Carbon, N₂ SA 142 m² /g)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Active agent: Diethyleneglycol

Silicone oil: KF 99 (Shinetsu Chemical Ind. Ltd.)

Zinc oxide: Zinc white #3 (Seido Kagaku)

Stearic acid: Lunac YA (Kao Soap Co.)

Antioxidant: Antigen 6C (Sumitomo Chemical Co.)(N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine)

Sulfur: Insoluble sulfur (20% oil treatment)

Vulcanization accelerator: Nocceler NS-F (Ouchi Shinko ChemicalIndustrial Co., Ltd.) (N-tert-butyl-2-benzothiazolylsulfenamide)

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece (rubbersheet) and the vulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties are as follows:

Mooney viscosity, Scorching time, Vulcanization rate

Tested in the same methods as in Example I

E' (storage modulus) and tanδ

The measurement was carried out using viscoelasticity spectrometer (madeby Toyo Seiki Seisakusho) under the conditions of a temperature of 60°C., an initial strain of 10%, a dynamic strain of ±2% and a frequency of20 Hz.

The following evaluation results are shown in Table V, together with thecompounding compositions. Note that Comparative Example III-1 is atypical conventional composition for a bead filler.

Examples III-1 to III-7 are all within the range of the presentInvention and all provide the good results. Especially, Examples III-6and III-7, in which silica is used together with carbon black, by thecompounding of the polysiloxane, the decrease in the viscosity of theunvulcanized compounding composition and the extension of the scorchingtime were observed, the vulcanization rate is shortened, theprocessability and productivity are made good and, in the vulcanizateproperties, tanδ is further decreased and the durability is improved,without substantially impairing E' (storage modulus). Note thatComparative Example III-2 in which the silicone oil is contained, thevulcanized rubber sheet was foamed and was not able to be practicallyused.

As explained above, according to the third embodiment of the presentinvention, by compounding 50 parts by weight or more of the specifiedcarbon black and 0.1 to 10 parts by weight of the specified polysiloxaneto 100 parts by weight of the diene rubber containing 40 parts by weightor more of natural rubber, the desired results such as the improvementsin the processability by the decrease in the viscosity and the extensionin the scorching time (prevention of the burning of the rubber in theextrusion and pressing steps, the increase in the line speed, etc.), orthe improvement in the productivity by the shortening of thevulcanization step, without impairing the physical properties of thevulcanizate such as E' (storage modulus) and tanδ. Thus, the rubbercomposition according to the present invention is suitable for use asthose for bead filler of tires for passenger cars, trucks and buses.

Example IV-1 to IV-10 and Comparative Examples IV-1 to IV-5

The polysiloxane 1 and 2 used in the following Examples were synthesizedaccording to the method described in Example I.

The other compounding components used in the compounding of thefollowing Examples and Comparative Examples (see Table VI) were thefollowing commercially available products.

                  TABLE VI                                                        ______________________________________                                                   (wt. parts)                                                                     Comp.                                                              Example Example                                                                          IV-1    IV-2    IV-1  IV-2  IV-3                                 ______________________________________                                          NR 40 40 40 40 50                                                             BR 60 60 60 60 50                                                             Carbon black-1 --  -- -- -- --                                                Carbon black-2 50 30 30 30 30                                                 Carbon black-3 -- -- -- -- --                                                 Silica -- 20 20 20 20                                                         Silane coupling -- 2.0 1.0 1.0 1.0                                            agent                                                                         Polysiloxane-1 -- -- 1.0 3.0 1.0                                              Polysiloxane-2 -- -- -- -- --                                                 Silicone oil -- -- -- -- --                                                   Active agent -- 1.3 1.3 1.3 1.3                                               Aromatic oil 15 15 15 15 15                                                   Zinc white 3.0 3.0 3.0 3.0 3.0                                                Stearic acid 2.0 2.0 2.0 2.0 2.0                                              Antioxidant-1 3.0 3.0 3.0 3.0 3.0                                             Antioxidant-2 2.0 2.0 2.0 2.0 2.0                                             Wax 1.5 1.5 1.5 1.5 1.5                                                       Sulfur 1.5 1.5 1.5 1.5 1.5                                                    Vulcanization 1.0 1.0 1.0 1.0 1.0                                             agent                                                                         tanδ (60° C.) 0.21 0.17 0.17 0.17 0.18                           Flex 100 110 115 117 109                                                      fatigue (index)                                                               Mixing 5 3 5 5 5                                                              processability                                                              ______________________________________                                                   (wt. parts)                                                          Example                                                                                  IV-4    IV-5    IV-6  IV-7  IV-8                                 ______________________________________                                          NR 40 40 40 40 40                                                             BR 60 60 60 60 60                                                             Carbon black-1 -- -- -- -- 30                                                 Carbon black-2 -- 40 30 30 --                                                 Carbon black-3 30 -- -- -- --                                                 Silica 20 10 20 20 20                                                         Silane coupling 1.0 0.5 -- 2.0 1.0                                            agent                                                                         Polysiloxane-1 1.0 0.5 -- 2.0 1.0                                             Polysiloxane-2 -- -- 1.0 -- --                                                Silicone oil -- -- -- -- --                                                   Active agent 1.3 0.7 1.3 1.3 1.3                                              Aromatic oil 10 15 15 15 15                                                   Zinc white 3.0 3.0 3.0 3.0 3.0                                                Stearic acid 2.0 2.0 2.0 2.0 2.0                                              Antioxidant-1 3.0 3.0 3.0 3.0 3.0                                             Antioxidant-2 2.0 2.0 2.0 2.0 2.0                                             Wax 1.5 1.5 1.5 1.5 1.5                                                       Sulfur 1.5 1.5 1.5 1.5 1.5                                                    Vulcanization 1.0 1.0 1.0 1.0 1.0                                             agent                                                                         tanδ (60° C.) 0.14 0.19 0.17 0.17 0.22                           Flex 112 106 114 110 111                                                      fatigue (index)                                                               Mixing 5 5 5 5 5                                                              processability                                                              ______________________________________                                                   (wt. parts)                                                                     Comp. Example   Example                                                       IV-3    IV-4    IV-5  IV-9  IV-10                                ______________________________________                                          NR 40 40 80 40 40                                                             BR 60 60 20 60 60                                                             Carbon black-1 --  -- -- -- --                                                Carbon black-2 30 30 30 50 50                                                 Carbon black-3 -- -- -- -- --                                                 Silica 20 20 20 -- --                                                         Silane coupling -- 1.0 1.0 -- --                                              agent                                                                         Polysiloxane-1 -- -- 1.0 2.0 4.0                                              Polysiloxane-2 -- -- -- -- --                                                 Silicone oil -- 1.0 -- -- --                                                  Active agent 1.3 1.3 1.3 -- --                                                Aromatic oil 15 15 15 13 11                                                   Zinc white 3.0 3.0 3.0 3.0 3.0                                                Stearic acid 2.0 2.0 2.0 2.0 2.0                                              Antioxidant-1 3.0 3.0 3.0 3.0 3.0                                             Antioxidant-2 2.0 2.0 2.0 2.0 2.0                                             Wax 1.5 1.5 1.5 1.5 1.5                                                       Sulfur 1.5 1.5 1.5 1.5 1.5                                                    Vulcanization 1.0 1.0 1.0 1.0 1.0                                             agent                                                                         tanδ (60° C.) 0.17 -- 0.19 0.21 0.21                             Flex 96 -- 83 104 109                                                         fatigue (index)                                                               Mixing 3 2 5 5 5                                                              processability                                                              ______________________________________                                    

Natural Rubber: SIR-20 (Tg: -71° C.)

BR: Nipol 1220 (Nihon Zeon) (Tg: -106° C.)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Carbon black

CB-1: Diablack A (Mitsubishi Chemical, N₂ SA 142 m² /g DBP oilabsorption=116 ml/100 g)

CB-2: Seast N (Tokai Carbon, N₂ SA 74 m² /g, DBP oil absorption=101ml/100 g)

CB-3: Diablack E (Mitsubishi Chemical, N₂ SA 41 m² /g DBP=115 ml/100 g)

Silicone oil: KF 99 (Shinetsu Chemical Industries Ltd.)

Active agent: Diethyleneglycol

Wax: Sannoc (Ouchi: Shinko Chemical Industrial Co., Ltd.)

Zinc oxide: Zinc white #3 (Seido Kagaku)

Stearic acid: Lunac YA (Kao Soap Co.)

Antioxidant-1: Antigen 6C (Sumitomo Chemical Co.)(N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine)

Antioxidant-2: Antigen RD (Sumitomo Chemical Co.)(poly-(2,2,4-trimeltyl-1,2-dihydroquinoline)

Vulcanization accelerator: Nocceler CZ (Ouchi Shinko Chemical IndustrialCo., Ltd.) (N-cyclohexyl-2-benzothiazylsulfenamide)

Sulfur: A 5% oil treated powder sulfur

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece (rubbersheet) and the vulcanized physical properties were evaluated.

The test and evaluation methods for the composition in each Example areas follows.

tanδ (60° C.)

Measured by viscoelasticity spectrometer (made by Toyo Seiki Seisakusho)at 60° C. initial strain of 10%, dynamic strain of ±2%, and 20 Hz. Asthe value becomes smaller, the hysteresis less tends to decrease and therotating resistance of a tire can be decreased.

Flexfatigue

The measurement was carried out until the failure using a fatigue testmachine (made by Monsanto Co.) by a method according to ASTM-D-4482except that the condition of a distortion rate of 120%. The number oftimes until the failure was shown indexed to that of Comparative ExampleIV-1 as 100. The larger the value, the better the anti-flexfatigue.

Mixing Processability

The kneading performance and sheeting properties of the blended rubber,the dispersion conditions of carbon black/silica were visually evaluatedby mixing under the mixing method and mixing conditions similar to thosewhen preparing the above-mentioned samples and evaluated by 5 point fullmark (i.e., point 5: best).

The evaluation results are shown in Table VI, together with thecompounding composition.

Comparative Example IV-1 is an example of the typical conventionalcompound for a side tread, Comparative Example IV-2 contains the silicaand the coupling agent, in addition to Comparative Example IV-1 as abase, but the processability is not sufficient. Examples IV-1 to IV-6exhibit the decrease in the heat generation (tanδ), good flex fatigueproperty, and no problem in the processability. Example IV-7 containingonly the polysiloxane (i.e., no coupling agent), compared with ExampleIV-1, exhibits a minor decrease in the flex fatigue, but no problem inthe processability. Comparative Example IV-3 containing neither thepolysiloxane nor the coupling agent exhibits the poor flex fatigue andprocessability. Comparative Example IV-4 containing the silicone oil, inaddition to the composition of Example IV-1, exhibits that the rubbersheet was foamed and was not able to practically used. ComparativeExample IV-5 contains the polymer blend which is not within thedefinition of the polymer of the present invention, when compared withExample IV-1, and therefore, exhibits the poor flex fatigue property.Comparative Example IV-6 contains the carbon black, which is not withinthe definition according to the present invention, when compared withExample IV-1, and exhibits the poor heat generation. Examples IV-9 andIV-10 according to the present invention are those containing no silica,when compared with Comparative Example IV-1, and exhibit good flexfatigue property, without impairing the processability and the heatgeneration.

As explained above, according to the fourth embodiment of the presentinvention, the rolling resistance of the vulcanizate can be decreasedand the flex resistance can be increased, as a rubber composition for atire tread, without substantially causing a change for the worse in themixing processability and the dispersibility.

Examples V-1 to V-7 and Comparative Examples V-1 to V-5

The polysiloxanes used in the present invention were synthesizedaccording to the method described in Example I.

The other compounding components used in the compounding of thefollowing Examples and Comparative Examples (see Table VII) were thefollowing commercially available products.

                                      TABLE VII                                   __________________________________________________________________________           Comp.                           Comp.                                                                             Comp.                                                                             Comp.                                                                             Comp.                        Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam-       ple ple ple ple ple ple ple ple ple ple ple ple                               V-1 V-1 V-2 V-3 V-4 V-5 V-6 V-7 V-2 V-3 V-4 V-5                             __________________________________________________________________________    IIR    75  75  75  75  75  55  75  75  75  75  75  75                           NR 25 25 25 25 25 45 25 25 25 25 25 25                                        CB-1 60 60 60 60 60 60 30 30 60 --  60 50                                     CB-2 --  --  --  --  --  --  --  --  --  60 --  --                            Silica -- -- -- -- -- -- 20 20 -- --  -- --                                   Silane coupling -- -- -- -- -- -- 1.0 --  -- -- -- --                         agent                                                                         Active Agent -- -- -- -- -- -- 1.3 1.3 -- -- -- --                            Polysiloxane-1 -- 1.0 2.0 4.0 -- 2.0 2.0 2.0 -- 2.0 -- --                     Polysiloxane-2 -- --  --  --  2.0 --  --  --  -- --  -- --                    Silicone oil -- -- -- -- --  -- -- -- 2.0 -- -- --                            Aromatic oil 4.0 3.0 2.0 -- 2.0 3.0 1.0 -- 2.0 7.0 9.0 4.0                    Zinc oxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0                    Stearic acid 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                  Sulfur 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8                        Vulcanization 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                 agent                                                                         Mooney 66 64 61 57 62 62 62 63 65 65 62 62                                    viscosity                                                                     Scorching 19 20 21 22 21 22 21 22 18 20 20 21                                 time (min)                                                                    Vulcanization 17.9 17.3 17.1 16.8 17.2 16.4 17.2 17.4 16.1 17.3 18.4                                                           18.6                         rate (min)                                                                    E' (MPa) 3.0 3.0 3.0 3.0 3.0 3.0 3.1 3.1 -- 3.0 2.6 2.5                       (60 C°)                                                                tanδ (60° C.) 0.18 0.18 0.18 0.18 0.18 0.17 0.16 0.16 --                                                          0.21 0.19 0.17             __________________________________________________________________________

Butyl rubber IIR: Brominated isobutyrene isoprene rubber (ExxonBromobutyl Rubber 2244)

Natural rubber NR: SIR-20

Carbon black

CB-1: Seast V (Tokai Carbon, N₂ SA 27 m² /g)

CB-2: Seast 300 (Tokai Carbon, N₂ SA 84 m² /g)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Silicone oil: KF99 (Shinetsu Chemical Industries Ltd.)

Aromatic oil: Process oil X-140 (Kyodo Sekiyu)

Zinc oxide: Zinc white #3 (Seido Kagaku)

Stearic acid: Lunac YA (Kao Soap Co.)

Sulfur: Oil treated sulfur

Vulcanization accelerator: Suncellar DM (Sanshin Chemical)(Dibenzothiazyldisulfide)

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece (rubbersheet) and the vulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties are as follows.

Mooney Viscosity, Scorching Time and Vulcanization Rate

The tests were carried out in the same procedures as those of Example I.

E' (Storage Modulus) and tanδ

The tests were carried out in the same procedures as those of Example I.

The following evaluation results are shown in Table VII, together withthe compounding compositions. Note that Comparative Example V-1 is atypical conventional compounding composition for an inner liner.

Examples V-1 to V-7 are compounding compositions within the scope of thepresent invention and all provides the good results. Namely, ExamplesV-1 to V-5 are those containing the polysiloxane with respect toComparative Example V-1 and the decrease in the viscosity and theextension of the scorching time of the unvulcanized compoundingcomposition are observed and the vulcanization rate is shortened, theprocessability becomes good, without substantially impairing thephysical properties of the vulcanizate of E' (storage modulus) and tanδ.Examples V-6 and V-7 are those containing the silica, in addition tothat of Example V-2, and the heat generation is decreased and it ispreferable from the viewpoint of the durability.

On the other hand, Comparative Example V-2 contains silicone oil,instead of the polysiloxane of Example V-2, the rubber sheet was foamed,and therefore, this was not practically used. Comparative Example V-3uses the polymer blend, which is the outside of the definition thereofin the present invention, when compared with Example V-2, and therefore,the heat generation becomes worse (i.e., the increase in tanδ).Comparative Examples V-4 to V-5 contain the increased amount of theprocess oil and the decreased amount of the carbon black, when comparedwith Example V-2, so as to intend to decrease the viscosity, but this isnot preferable from the viewpoint of the durability because E' (storagemodulus) is decreased.

As explained above, according to the fifth embodiment of the presentinvention, the desired results such as the decrease in the viscosity ofthe unvulcanized compounding composition, the improvement in theprocessability by the extension of the scorching time (prevention of theburning of the rubber in the extrusion and pressing steps, the increasein the line speed, etc.), or the improvement in the productivity by theshortening of the vulcanization step can be obtained, without impairingthe physical properties of the vulcanized products such as E' (storagemodulus), tanδ, etc. due to the compounding 20-120 parts by weight ofthe specified carbon black and 10 parts by weight or less of thespecified polysiloxane to 100 parts by weight of the rubber componentcontaining 50 parts by weight or none of butyl rubber and 50 parts byweight or less of diene rubber. Thus, the rubber composition accordingto the present invention is suitable for use as those for an inner linerof a tire for a passenger car, truck, bus.

Examples VI-1 to VI-5 and Comparative Examples VI-1 to VI-8

The polysiloxanes used in the present invention were synthesizedaccording to the method described in Example I.

The other compounding components used in the compounding of thefollowing Examples and Comparative Examples (see Table VIII) were thefollowing commercially available products.

                                      TABLE VIII                                  __________________________________________________________________________           Comparative             Comparative                                      Example Example Example                                                            VI-1                                                                             VI-2                                                                             VI-1                                                                             VI-2                                                                             VI-3                                                                             VI-4                                                                             VI-5                                                                             VI-6                                                                             VI-3                                                                             VI-4                                                                             VI-5                                     __________________________________________________________________________    NR     70 70 70 70 70 70 70 70 70 70 70                                         SBR 30 30 30 30 30 30 30 30 30 30 30                                          Carbon black 80 80 80 80 80 80 80 80 80 80 80                                 Clay-1 50 --  50 50 50 50 50 --  50 50 50                                     Clay-2 --  40 --  --  --  --  --  40 --  --  --                               Silane -- --  -- -- -- -- 3.0 --  -- -- --                                    coupling agent                                                                Polysiloxane-1 -- -- 1.0 2.0 4.0 -- 2.0 2.0 -- -- --                          Polysiloxane-2 -- -- --  --  --  2.0 --  --  -- -- --                         Silicone oil -- --  -- -- --  -- -- 2.0 -- --                                 Aromatic oil 10.0 10.0 9.0 8.0 6.0 8.0 8.0 8.0 8.0 15.0 10.0                  Zinc oxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0                        Stearic acid 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0                      Sulfur 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0                            Vulcanization 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                     accelerator                                                                   Mooney 54 57 52 50 45 51 51 52 54 51 52                                       viscosity                                                                     Scorching 24 22 25 26 27 26 25 25 23 25 25                                    time (min)                                                                    Vulcanization 9.3 9.2 9.1 9.0 8.8 9.0 8.8 9.0 8.5 9.5 9.4                     rate (min)                                                                    Hs (20° C.) 76 77 76 76 76 76 77 77 --  73 74                          TB (MPa) 14.2 16.0 14.2 14.2 14.1 14.2 14.9 16.1 -- 13.9 14.0                 EB (%) 270 260 275 280 285 275 285 270 -- 295 285                           __________________________________________________________________________

Natural Rubber: RSS #3

SBR: Nipol 1502 (Nihon Zeon)

Carbon black: Seast V (Tokai Carbon)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Silicone oil: KF 99 (Shinetsu Kagaku Kogyo K.K.)

Aromatic oil: Process oil X-140 (Kyodo Sekiyu)

Zinc oxide: Zinc white #3 (Seido Kagaku)

Stearic acid: Lunac YA (Kao Soap)

Sulfur: Insoluble sulfur (20% oil treatment)

Vulcanization accelerator: Nocceler-NS-F (Ouchi Shinko ChemicalIndustrial Co., Ltd.) (N-tert-butyl-2-benzothiazolyl-sulfenamide)

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a closed type mixer for more than 3 minutes. Thevulcanization accelerator and sulfur were kneaded by an open roll to themaster batch which was discharged from the mixer when reaching 165±5° C.to obtain the rubber composition. The unvulcanized physical propertiesof the rubber composition thus obtained were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the intended test piece (rubbersheet) and the vulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties are as follows.

Mooney viscosity, Scorching time, Vulcanization rate, Hardness Hs

Measurements were carried out in the same procedures as those of ExampleI.

Tearing strength at break (TB) and Elongation at break (EB)

The tensile strength at break (TB) and the elongation at break (EB) weredetermined at a temperature of 25° C. according to JIS-K6301.

The following evaluation results are shown in Table VIII, together withthe compounding compositions. Note that Comparative Example VI and VIIare typical conventional compositions containing clay.

Examples VI to VI-4 are those containing the polysiloxane in addition toComparative Example VI-1, the vulcanized physical properties of thehardness, the tensile strength and the elongation are comparative ormore, with respect to Comparative Example VI-1, and the decrease in theviscosity, the extension of the scorching time and the shortening of thevulcanization rate are observed and the improvement in theprocessability is also observed. Example VI-5 contains the couplingagent, in addition to Example VI-2, and therefore, the improvements inthe hardness, the tensile strength and the elongation are observed.Example VI-6 additionally contains the polysiloxane according to thepresent invention, when compared with Comparative Example VI-2, andtherefore, the results similar to those of Examples VI-1 to VI-4 areobserved.

On the other hand, Comparative Example VI-3 contains the silicone oilwith respect to Example VI-2, and the rubber sheet was foamed andtherefore was not able to be practically used. Comparative Examples VI-4to VI-5 are those containing the increased amount of the oil and thedecreased amount of the carbon black, compared with the Example, for theintention of decreasing the viscosity, but this is not preferablebecause the hardness and the tensile strength are also decreasedalthough the viscosity is decreased.

As explained above, according to the sixth embodiment of the presentinvention, the desired results such as the decrease in the viscosity ofthe unvulcanized compounding composition, the improvement in theprocessability by the extension of the scorching time (prevention of theburning of the rubber in the extrusion and pressing steps, the increasein the line speed, etc.), or the improvement in the productivity by theshortening of the vulcanization step can be obtained, without impairingthe physical properties of the vulcanized products such as the hardness,the tensile strength TB etc. due to the compounding of the polysiloxaneto the clay-containing rubber composition. Thus, the resultantclay-containing rubber composition according to the present invention issuitable for use as a rubber composition for bead insulation or whileside tread of a tire for a passenger car, truck or bus.

What is claimed is:
 1. A rubber composition for a tire comprising:100parts by weight of a starting rubber; 10 to 150 parts by weight of acarbon black; 0.1 to 20 parts by weight of a sulfur; and 0.01 to 40parts by weight or less of a polysiloxane having the followingalkoxysilyl group (I) or acyloxysilyl group (II) and having an averagedegree of polymerization of 3 to 10,000:

    .tbd.Si--OR.sup.1                                          (I)

    .tbd.Si--OCOR.sup.2                                        (II)

wherein R¹ is a substituted or unsubstituted monovalent hydrocarbongroup or an organic group containing an ether bond and having 1 to 18carbon atoms and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.
 2. A rubber composition for covering a steel cord asclaimed in claim 1, wherein the starting rubber is 100 parts by weightof a diene rubber containing 40 parts by weight or more of naturalrubber and the amount of the polysiloxane is 0.01 to 10 parts by weight.3. A rubber composition as claimed in claim 2, wherein 0 to 2 parts byweight, in terms of a Co element, of a cobalt salt of an organic acid iscontained in the composition.
 4. A rubber composition as claimed inclaim 2 or 3, wherein the composition further comprises 1.0 to 5 partsby weight of partial self-condensation product of hexamethylolmelaminepentamethyl ether and 0.5 to 5 parts by weight of a cresol resin.
 5. Arubber composition for a carcass or belt cover as claimed in claim 1,wherein the starting rubber is 100 parts by weight of a diene rubbercontaining 40 parts by weight or more of natural rubber, the carbonblack is 20 to 120 parts by weight of a carbon black having a nitrogenspecific surface area of no more than 60 m² /g and the amount of thepolysiloxane is 0.01 to 10 parts by weight.
 6. A rubber composition fora tire bead filler as claimed in claim 1, wherein the starting rubber is100 parts by weight of a diene rubber containing 40 parts by weight ormore of natural rubber, the carbon black is 50 parts by weight or moreof a carbon black having a nitrogen specific surface area of no morethan 100 m² /g, and the amount of the polysiloxane is no more than 10parts by weight.
 7. A rubber composition for a tire side tread asclaimed in claim 1, wherein the starting rubber is 100 parts by weightof a diene rubber containing 40 parts by weight or more ofpolybutadiene, 5-50 parts by weight of silica and 10-60 parts by weightof carbon black are included in the total amount of the silica and thecarbon black is 20-80 parts by weight, and the polysiloxane having atleast 6 alkoxy groups or at least 2 acyloxy groups directly bonded tothe Si atom in the molecule thereof and having an average degree ofpolymerization of 3-10,000 in an amount of 0.01 40% by weight based uponthe amount of the silica.
 8. A rubber composition as claimed in claim 7,wherein no more than 40% by weight, based upon the amount of the silica,of a silane coupling agent is further contained.
 9. A rubber compositionas claimed in claim 7 or 8, wherein the carbon black has a nitrogenspecific surface area (N₂ SA) of no more than 100 m² /g and a DBP oilabsorption of 70 ml/100 g or more.
 10. A rubber composition for an innerliner rubber as claimed in claim 1, wherein the starting rubber is 100parts by weight of a rubber component containing 50 parts by weight ormore of butyl rubber and no more than 50 parts by weight of a dienerubber, the carbon black is 20 to 120 parts by weight of a carbon blackhaving a nitrogen surface area of no more than 60 m² /g, and the amountof the polysiloxane is 0.01 to 10 parts by weight.
 11. A claycompounding rubber composition as claimed in claim 1, wherein 5 to 100parts by weight, based upon 100 parts by weight of the starting rubber,of clay and the amount of the polysiloxane is 0.01 40% by weight basedupon the amount of the clay.
 12. A process for applying a rubbercomposition according to claim 1 for covering a steel cord of a tire.13. A process as claimed in claim 12, wherein the starting rubber is 100parts by weight of a diene rubber containing 40 parts by weight or moreof natural rubber and the amount of the polysiloxane is 0.01 to 10 partsby weight.
 14. A process as claimed in claim 12, wherein 0 to 2 parts byweight, in terms of a Co element, of a cobalt salt of an inorganic acidis contained in the composition.
 15. A process as claimed in claim 12,wherein the composition further comprises 1.0 to 5 parts by weight ofpartial self-condensation product of hexamethylolmelamine pentamethylether and 0.5 to 5 parts by weight of a cresol resin.